Michael Tilson Thomas and the San Francisco Symphony have begun their two-week Beethoven festival, dubbed the "Beethoven Project." One of its goals is scholarly: to connect the dots between some of the titan's early rarities and his late-period ascensions. But, basically, what Thursday's opening program accomplished was to make your jaw drop.

The program -- the first of its two performances -- was devoted to those youthful rarities, including "some really oddball stuff," which is how John Mangum, the orchestra's director of artistic planning, put it in a pre-concert talk. The most oddball was the Sonatina in C major for Mandolin and Fortepiano, sort of a 19th-century bluegrass prophecy; more on that later. The jaw-dropper was the Cantata on the Death of the Emperor Joseph II, a massive work for orchestra, chorus and four soloists, which points toward much later masterworks -- and which Beethoven composed at age 19.

Composed in 1790 -- after the passing of the Holy Roman Empire's monarch -- this grand endeavor stretches across 40 minutes. (You may recognize some of its themes; Beethoven recycled them into "Fidelio.")

There are moments, quite a few, when teenaged Beethoven strains for portent; the steady declamations of world-weariness and grief feel a little faux. Yet there are many sublime effects, and the maturity of the orchestration is astonishing: trembling cross-currents in the strings that verily "speak" Beethoven; likewise, a delicate chorale for winds; and the entwining of solo voices, chorus and instrumental forces, all commandingly marshaled by Tilson Thomas, making for a vast and expressive emotional matrix.

Beethoven assigns two central arias and a recitative to the soprano, and Matthews lived up to her star billing. One could listen all night to her singing: exquisite, plush and very mezzo-y. She traced the curve of Beethoven's swan's-neck melodies, conveying their deep solace. Her first aria seemed predictive of Brahms' Alto Rhapsody; interesting, as Brahms was a fan of this cantata, which was first performed in 1884, long after Beethoven's death.

The gravity of this work stood in contrast to the one preceding it: "Adelaide," a song from 1796, setting verse by German Romantic poet Friedrich Matthisson and exuding a young man's pure-hearted love of a woman. Composed by Beethoven for piano and voice, it has been newly arranged for chorus by Bohlin, who conducted. (The sole instrumentalist was principal keyboardist Robin Sutherland, playing Beethoven's original piano part, superbly.)

These expanded accolades for "Adelaide" were gorgeous: love's rustlings and murmurs, echoing and lapping through the chorus. Oh, Adelaide!

After intermission, as the house lights dimmed and patrons rushed to their seats, it was time for the "oddball" stuff: mandolinist Joseph Brent and fortepianist Eric Zivian were spot-lit in a far corner of the stage, looking as if they had wandered in from one of Wes Anderson's film sets. They launched into the aforementioned Sonatina; a quiet, quirky and charming performance. And very folkish; its finger-picking principal theme is a bluegrass forerunner. Who knew?

This imaginative program concluded with something more familiar: Symphony No. 2 in D major, which the orchestra was recording for future release on CD. To these ears, the spacious opening movements weren't vivid enough; Tilson Thomas was locked into a dynamic mid-range. The Scherzo was elegant, somewhat slower and less comically exaggerated than in many performances. The finale was best, skewering that outrageous theme which sounds like Buster Keaton tumbling down a flight of stairs and leaping to his feet. For all his familiarity, Beethoven still surprises.